Ink transfer roller with interchangeable cover

ABSTRACT

An ink transfer roller for a support roller or support bar, in particular of metal, with a stretchable, interchangeable fiber-reinforced laminated plastic material cover (K) covered with a metal-ceramic layer (MK), which is provided with small ink transfer cups (FN), wherein the laminated plastic material cover (K) consists of a stretchable inner cover (UB) and an outer cover (OB), between which a foamed material compressible layer (SS) is enclosed.

This is a CIP of parent application Ser. No. 08/343,932, filed Nov. 17,1994, now abandoned the contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to an ink transfer roller especially foruse with a support roller or support bar, in particular of metal, with astretchable, interchangeable fiber-reinforced plastic laminated materialcover in turn covered with a metal-ceramic layer, which is provided withsmall ink transfer cups.

BACKGROUND OF THE INVENTION

Prior-art ink transfer rollers having a cover over a metal roller haveheretofore used a cover in the form of a cylindrical, one-piece body oflaminated synthetic resin material equipped with fiberglass mat inserts,supporting on its surface a metal-ceramic layer with small ink transfercups cut in by laser. This fiberglass-mat reinforced epoxy resin body isexpanded by means of compressed air and pulled over the steel rollerbody and maintained there by elastic radial forces. However, afterprolonged use the elastic tension relaxes because of the increasedoperating temperature, by reason of a flexing expansion of the plasticjacket.

However, corrosion of the surface of the metal roller can be caused bythe penetration of printing ink and an excursion of the cover can takeplace, which in particular drastically worsens the ink transfer qualityand is therefore unacceptable. In addition, the synthetic resin surfacewhich had been ground and polished before being ceramized has tiny poreswhere the glass fibers were cut on the surface, sources of incipientcorrosion.

Ink transfer rollers with layers made of a metallic matrix with aninsert material of a mechanically resistant metal-ceramic material, forexample nickel-silicon carbide, are known, which have a very highstability of the laser-cut small ink transfer cups.

One such ink transfer roller is known, for instance, from German PatentDisclosure DE 40 07 130 A1. In it, cups are impressed into a metalsurface, and a burr created in the process is removed. To increase theabrasion resistance, the cup surface is galvanically coated with hardmaterial such as hard chromium, or with particles of silicon carbideembedded in a nickel matrix; an additional, thin layer of hard chromiumcan be applied over this. However, these upper layers are always shotthrough with fine microscopic cracks, and fine pores in the micrometerrange can be found especially in the boundaries of the inlaid particlesof hard material, resulting in only limited adhesion thereof.

Inking rollers are also known from the journal Flexo, 1985, Vol. 10, No.10, pp. 45-50, whose cups are laser-cut into a plasma-sprayed hardceramic layer, such as chromium oxide, Cr₂ O₃. Spotwise high-temperaturetreatment with the laser beam and the ensuing rapid cooling result inmicroscopic cracks, microscopic pores, and major distortions and strainsin the microstructure, which lessens the abrasion resistance andcorrosion resistance.

SUMMARY OF THE INVENTION

Objects of the invention are to overcome deficiencies in the prior art,such as indicated above; and to improve the service life and stabilityof the ink transfer roller. These objects are attained by providing acover of plastic laminated material which consists of a stretchableinner cover and an outer cover, between which a layer of foamed materialis enclosed.

By means of the elastic interlayer, the essentially three-layeredembodiment of the plastic cover prevents a transfer of the flexingmotion to the inner cover which, because of this, always adheres tightlyand solidly to the support roller. Furthermore, the stretching by meansof compressed air which is applied from the interior to the inner coveris intercepted by the foamed material and is kept away to a large degreefrom the relatively brittle metal-ceramic layer, which reduces thecreation of micro-tears therein.

Furthermore, the cover does not contain glass fibers, particularly notat the surface, so that prior to ceramizing no corrosion centers andmicropores are present on the polished, preferably plasma-polished,surface.

According to the present invention, layer with a circular andaxis-parallel extension of the fibers, made of a microfiber-polyesterfabric, has shown itself to be especially advantageous as the insertmaterial for the inner cover, which therefore has sufficientstretchability with high stability of shape. A fabric with approximately15×15 flat aramid (aromatic polyamide, e.g. KEVLAR^(w) *w of Dupont)threads has proven to be advantageous for the insert; polyester can alsobe used. The softening point of this fabric lies above 120° C., so thatthe heat treatment during curing of the polyester resin, during plasmainjection as well as during operation in the printing presses, does notleave a permanent deformation.

The plastic web layers in the inner and outer covers are made oflong-fiber plastic threads and are each of approximately 0.5 mmthickness. They are soaked with the synthetic resin, the same as thefabric, and wound on top of each other and then cured. After the innercover has cured, the foamed material layer is wound on it and is thenwrapped with the synthetic resin-soaked webs of the outer cover and thencured, in the course of which the shrinking forces occurring during theprocess of solidification reduce the foamed material layer toapproximately one-half its original volume, so that a steady radialtension keeps all three layers together.

The foam rubber layer is preferably made of temperature-stable,closed-cell polyurethane, polypropylene or polyamide, the density ofwhich prior to installation is approximately 0.3 to 0.7 g/cm³.

Alternatively the three-layered construction can also be created bylayered extrusion of a thermoplastic material, for example polypropyleneor polyamide, wherein the interlayer is foamed by means of a partial gasinjection or by an expanding agent.

The outer layer is either made of a high-pressure plasma-injectedmetal-ceramic material, for example Cr₂ O₃ of a thickness of a fewtenths of a millimeter, and directly applied to the synthetic resinsurface or to a metallic adhesive layer preferably consisting of a thinmetallic layer, which is elastic and forms a moisture-sealed interlayer.

In place of a pure metal-ceramic layer it is also possible to apply ametallic matrix with embedded mechanically resistant materials. Theknown nickel-silicon carbide coating (a coating of silicon carbideparticles embedded in nickel) has proven itself.

It has been shown to be advantageous for preventing corrosion from thedirection of the ends to embody the outer cover and/or the inner coverwith annular rims at the ends, which close off the ends of the ceramiclayer in particular as well as the foamed material layer and prevent theinfiltration by ink material and their solvents.

The ink transfer roller of the present invention may have a surfacestructure, made mechanically or by laser action, of ink transfer cups(or, wells) in a microporous, metallic or ceramic or metal-ceramic layerof hard material, and to a method for producing it.

Another object of the invention is to improve the ink transfer rollerdescribed at the outset in such a way that it has a longer service life,less wear, and less vulnerability to corrosion.

This object is attained in that superficial microscopic cracks and poresin the ceramic layer are closed by means of an ion implant materialapplied with a high-voltage plasma.

All the microstructured ink transfer rollers known until now aresuitable for the treatment according to the invention with their surfacewith implant material, both in new production and in retrofitting. Thelayers of material applied in the implantation have, compared to the cupdimensions, a comparatively slight thickness of 1 to 2 μm, so that thecup volume remains virtually unchanged.

As materials for filling and closing the cracks and pores, combinationsof quadrivalent substances with heavy metal have proven to be good,especially quadrivalent titanium and hexavalent molybdenum in a ratio byweight of 70/30 to 90/10, and is preferably 80/20. These metal ionspenetrate deep into the interior of microscopic cracks and the boundarylayer that often occur at the particle boundaries of electrolyticallyapplied layers or sputtered layers, or after laser cutting. Inparticular, sealing and filling of the cracks increases the corrosionresistance, since the surface becomes smooth and dense.

The implantation of the metal ions is done in a nitrogen atmosphere, sothat the metals partly form compounds in the form of nitrides and formvery hard crystalline structures.

Advantageously, a further wear-resistant cover layer with a thickness offrom 0.05 to 1 μm, and preferably 0.1 μm of a hard material is implantedin a similar way. Hard metal oxides or metal nitrides are contemplatedfor this purpose. Zirconium oxide (ZrO₂) has proven to be especiallygood, and for this reason, the implantation is done in an oxygen plasma.This cover layer is selected in particular such that a desired surfaceaffinity with the printing ink to be transported and metered is broughtabout.

The implantations are done at high voltage with a turbulent flow of theplasma, preferably in nitrogen and/or oxygen. As the voltage, from 1000to 10,000 V are applied, and the current intensity is selected such thatwith moderate heating, an adequate penetration depth of the ions andanchoring of the implant in the surface take place without burning orthermally destroying the surface.

By suitable control of the current intensity and of the high voltage,the operating heat is kept so low that no significant thermal strainsarise in the layer near the surface, even after cooling down.Temperatures of from 50° to 80° C. are contemplated. As a result, evenrollers such as those disclosed in U.S. patent application Ser. No.08/343,932 can be hardened with an implant whose layer of hard materialis supported by a plastic understructure. In particular, the layer ofhard material is applied over a metal layer on an elastic plasticjacket, which comprises plastic reinforced with plastic fiber inlays,and which is interchangeably slipped, with an elastic understructure,onto a solid metal roller core.

The above and other objects and the nature and advantages of the presentinvention will become more apparent from the following detaileddescription of a preferred embodiment, taken with the drawing, wherein:

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view taken on a plane perpendicular to theaxis of a roller, i.e., showing a cut-out of a sector of a radial cut ofthe roller;

FIG. 2 is a cross-sectional view taken on a plane intersecting the axisof a roller, i.e., showing an enlarged axial cut at the front of theroller.

FIG. 3 is a section, enlarged 1000 times, through the microstructurebelow an impressed cup;

FIG. 4 is a highly enlarged section through a cup with a hard materialand metal matrix coating;

FIG. 5 shows a cross section enlarged 350 times.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following Description and claims, the term "metal-ceramic" meansceramic material crystallized from oxides, carbides, and/or nitrides ofheavy metals (defined as those metals heavier than Na), and excludingceramic compounds of alkali and alkali-earth metals (i.e., Li, Na, K,Rb, Cs, Fr, Be, Mg, Ca, Sr, Ba, and Ra).

In the following description and claims, "matrix" or "metallic/particlematrix" means a metallic/particle matrix containing hard particles suchas for example ceramic particles, i.e. a composite of metal and hardparticles.

FIG. 1 shows a portion of a radial section. The plastic laminatedmaterial cover (K) has been drawn over the metallic support roller (M)or a support arbor and is held by elastic radial forces. A thinmetal-ceramic layer (MK) has been applied on the exterior by means ofhigh-pressure plasma-extrusion, into which small ink transfer cups havebeen cut by laser in a known manner.

The plastic laminated material cover (K) consists of an inner cover (UB)of a synthetic resin laminated material containing a micro-fiber textilelayer (MF) of polyester micro-fibers with circular/axial extension ofthe fibers and contains further synthetic fiber web layers (KV). Thethickness of the inner layer (UB) is between 2 to 7 mm, preferably 3 mm.

The inner cover (UB) is wound in a foamed material layer (SS), thethickness of which is between 2 to 7 mm, preferably 4 mm when installed.

The outer cover (OB) of plastic fiber web layers with synthetic resinbonding is embodied over the foamed material layer (SS). That is, thelayers UB and OB are preferably made from a synthetic plastic (or resin)fiber web which is stabilized (laminated) in synthetic resin material.The metal-ceramic layer (MK) is applied to the ground and polishedsurface, if necessary by means of an adhesive layer, a metallicinterlayer (MS) The outer cover (OB) is preferably between 2 to 7 mmthick, in particular 3 mm. Around the entire cover (K) has a thicknessof approximately 10 mm.

FIG. 2 shows an axial section of a roller end. The outer cover (OB) hasa radially oriented annular rim (RR1), which tightly closes themetal-ceramic layer (MK) and, if required, the interlayer (MS)laterally.

In addition, the inner cover (UB) and/or the outer cover (OB) have asecond annular rim (RR2), which laterally seal(s) the foamed materiallayer (SS).

FIG. 3 shows a 1000-power enlargement of a small detail of the wall Wand bottom B of a cup N, in which the microstructure, comprising a hardmaterial HS, such as steel or the ceramic layer, is provided by means ofdoping in the micrometer range with an ion implant material H and acover layer D above it. This view clearly shows that the microstructureof the hard material HS is very extensively destroyed by the mechanicalmachining, and has great roughness and porosity on its surface eventhough the surface was electrolytically polished prior to the ionimplantation. The layer thicknesses of the implants H, D are shown withtheir heights exaggerated. In particular, the implanted oxide coverlayer D is generally substantially thinner than the nitrified metalimplantation H.

FIG. 4 shows an enlarged cross section into the surface of the roller;in a known manner, the cups N with an oxidic hard material HS, comprisea nickel matrix with carbide inlay over which a hard chromium layer isapplied. The chromium surface is then provided by the ion implantationwith the implant material H and the cover layer D.

FIG. 5 shows in a depth section, microscopic cracks or pores M extendinto the solidified cup surface into a great depth relative to the cupstructure. These microscopic cracks M are filled with the implant H. Thecover layer D is shown over the implant H; in particular, it favorablyaffects the compatibility of the ink with the surface and lends it apredetermined adhesive strength relative to the printing ink. Thethicknesses of the layers H and D are shown exaggerated.

The foregoing description of the specific embodiments reveal the generalnature of the invention so that others can, by applying currentknowledge, readily modify and/or adapt for various applications suchspecific embodiments without departing from the generic concept, and,therefore, such adaptations and modifications should and are intended tobe comprehended within the meaning and range of equivalents of thedisclosed embodiments. It is to be understood that the phraseology orterminology employed herein is for the purpose of description and not oflimitation.

What is claimed is:
 1. An ink transfer roller cover for demountablycovering a generally cylindrical roller surface and containing no classfibers at its surface, the roller cover comprising:a circumferentiallystretchable inner plastic layer (UB), the inner plastic layer beingproximal the roller surface when the roller cover is mounted to theroller surface; a foamed material compressible layer (SS) surroundingthe inner plastic layer; an outer plastic layer (OB) including asynthetic-plastic fiber web stabilized synthetic resin material incontact with and surrounding the compressible layer, the synthetic resinmaterial of the outer plastic layer including an elastic laminatedsynthetic resin material in which the fibers, having a thickness ofapproximately 0.5 mm, have been embedded as a plurality of syntheticresin web layers; a thin metal interlayer (MS) deposited on the outerplastic layer; and a metal ceramic layer deposited on the metalinterlayer, the metal ceramic layer including a plurality of inktransfer cups.
 2. The roller cover according to claim 1, wherein theceramic layer includes nickel-silicon carbide.
 3. The roller coveraccording to claim 1, wherein the inner plastic layer is between 2 and 7mm thick, and wherein the compressible layer includes an elasticclosed-cell foam selected from the group consisting of polyurethanefoam, polypropylene foam, and polyamide foam, and wherein thecompressible layer has a density between 0.3 to 0.7 g/cm³, and whereinthe compressible layer has a thickness of between 2 and 7 mm, andwherein the outer plastic layer has a thickness of between 2 to 7 mm. 4.The roller cover according to claim 1, wherein the outer plastic layerexerts a radial shrinking force on the compressible layer and on theinner plastic layer, whereby the roller cover is adhered to the rollersurface.
 5. The roller cover according to claim 1, wherein the outerplastic layer includes annular rims (RR1) projecting upwardly atopposing ends of the outer plastic layer to edge-seal the ceramic layer.6. The roller cover according to claim 5, wherein at least one of theouter plastic layer and the inner plastic layer includes annular rims(RR2) disposed at opposing ends of the compressible layer to edge-sealthe compressible layer.
 7. The roller cover according to claim 5,wherein the metal ceramic layer includes chromium oxide and the metallicinterlayer includes metal selected from the group consisting ofaluminum, tin, nickel, and copper.
 8. The roller cover according toclaim 5, wherein the metal ceramic layer and the metallic interlayer areapplied by high-pressure plasma-injection coating.
 9. The roller coveraccording to claim 1, wherein the inner plastic layer, the compressiblelayer, and the outer plastic layer are extruded in one piece fromlaminated plastic material with a foamed center layer.
 10. The rollercover according to claim 1, wherein superficial microscopic cracks (M)and pores in a surface of the metal ceramic layer with ink transfer cupsare closed by means of an ion implant material applied with ahigh-voltage plasma.
 11. The roller cover according to claim 10, whereinthe ion implant material comprises a quadrivalent substance and at leastone heavy metal.
 12. The roller cover according to claim 11, wherein theion implant material comprises titanium and molybdenum in a ratio offrom 70/30 to 90/10.
 13. The roller cover according to claim 10, whereinthe ion implant material is lined by means of ion implantation on anouter side thereof with a wear-resistant thin cover layer (D) of a hardmaterial selected from the group consisting of a metal oxide and a metalnitride, such that the cover layer (D) has a predetermined affinity fora printing ink to be metered with the printing roller.
 14. The rollercover according to claim 13, wherein the cover layer (D) has a thicknessof 0.05 to 1 μm.
 15. The roller cover according to claim 13, wherein thecover layer (D) comprises zirconium oxide.
 16. The roller coveraccording to claim 10, wherein the ceramic layer comprises ground andfinished chromium oxide Cr₂ O₃ in a thickness of from 100 to 150 μm, andcups (N) are made by laser engraving and finished, and subsequently theion implant material is inserted such that the pores are closed.
 17. Theroller cover according to claim 10, wherein the ceramic layer includesmetal-ceramic comprising a plasma-deposited nickel-chromium alloy in aratio of approximately 80/20 by weight, approximately 100 μm thick.